The present invention relates to a method used mainly for laser-initiated artillery propellant powder charges consisting of a plurality of propellant charge modules arranged one after another, of the so-called modular charge type, and for obtaining an even flash-over ignition of all the propellant charge modules included in the charge, in order thereby to eliminate the risks of uneven initiation and the occurrence of pendulum pressure. The invention also includes propellant charge modules and complete charges designed in accordance with the said method.
The type of propellant charge module in question here, so-called modular charges, consists very generally of a predetermined amount of propellant powder enclosed in a preferably rigid cylindrical container which is made of a combustible material and which is outwardly delimited by an outer cylinder wall adapted to the calibre dimensions of the artillery gun in question, two essentially plane and parallel gable walls defining its ends, and a centrally arranged inner cylinder wall which extends axially through the propellant charge module and which in turn defines a central ignition channel delimited from the propellant powder.
These modular charges are used without exception in combination in order to form propellant powder charges of a charge strength adapted to each range of fire.
A common feature of the modular charges is that they have an external diameter specific for each weapon and that they all have the previously mentioned central axial ignition channel which, when several modular charges are arranged in succession, for adaptation to a predetermined longer range of fire, will form a common and continuous ignition channel through all the modular charges included therein. By contrast, the modular charges can have different lengths and can contain different types and amounts of powder and can thereby have different charge strengths.
Among the advantages of these propellant charge modules, mention may be made of the fact that they are easy to combine into propellant charges of different charge strengths and are thus easily adapted to different ranges of fire, and, by virtue of their rigid configuration, they are easy to load automatically, which was not true of the soft, so-called bag charges, which they have been developed to replace.
As examples of the more general structure of the propellant charge modules of the xe2x80x9cmodular charge typexe2x80x9d in question here, reference may be made to U.S. Pat. No. 4,702,167, U.S. Pat. No. 4,864,932, U.S. Pat. No. 4,922,823 and WO 89/04453 where variations of these are described.
The most acute problem with artillery guns charged with modular charges has been found to be that it can be difficult to prevent initiation of the various modular parts of the charge being uneven when the piece is fired. This is because the initiation has to spread along the whole combined ignition channel of the charge where the different outer delimiting walls of the modular charges and the propellant charge powder in each modular charge for technical reasons will have slightly different burning characteristics.
The problem is well known within the sector and various proposals have previously been made for modular charges provided with specific firing charges intended to give an instant flash-over ignition alone the whole central ignition channel common to all the propellant charge modules. These previous solutions to the problem generally entail that each modular charge be provided, not just with the combustible central tube forming the central ignition channel, but also with firing charges of specially fast-burning material which bear against the inside of the central tube and are intended to spread the ignition along the whole of the continuous ignition channel of the complete charge before the respective central tube has had time to burn through. As an example of this prior art technique, reference may be made to U.S. Pat. No. 4,702,167, according to which the ignition channel of the modular charge is filled with a large number of special annular firing charges arranged in close succession. Another variant on the same theme is described in EP-0718591, although this proposes that the firing charge consists of several different layers of pyrotechnic material with different pore structures, the pores becoming ever closer towards the inner tube.
Finally, SE-9702949-0 describes a firing charge consisting of a limited number of annular firing charges concentrated in the central part of the ignition channel of each modular charge, where each firing charge ring has, alone at least one gable end directed towards the adjacent firing charge, a number of bosses or nibs which give rise to a narrow ignition gap between the different firing charge rings.
A problem which has hitherto been discussed very little in the context of modular charges is the difficulty in using laser to initiate this type of charge. It has in fact been found that laser initiation is even more locally limited than the result of conventional ignition cartridges, and laser initiation has therefore a greater tendency to give rise to uneven initiation. By contrast, general use of laser for initiation of the propellant powder charges in an artillery system should automatically entail that one is no longer dependent on special ignition cartridges, since the laser initiation system is in such cases incorporated in the actual artillery gun. Provided that the problem of uneven initiation can be solved, the laser initiation technique should therefore offer many advantages both as regards logistics and the speed with which the artillery gun in question will be able to be made ready for the next firing. At the same time, the modular charges adapted for laser initiation will also be able to be used without any disadvantage in those artillery guns where use is made of a conventional firing by ignition cartridge.
The object of the present invention is now to propose a method for obtaining an even flash-over ignition within and between standard modular charges which are designed such that the result is equally advantageous regardless of whether the initiation is done by laser or ignition cartridge. The invention also includes modular charges designed in accordance with this method, and complete artillery powder charges made up of these modular charges.
The problem which it has been possible to solve with the present invention is, as has already been stated, that of being able to eliminate the tendencies towards even initiation of propellant powder, primarily in those propellant powder charges which consist of a plurality of unit charges enclosed in combustible casings arranged one after another in a row and of the type which are usually called modular charges and which are fired using a laser initiation system, even though they are also suitable for initiation by conventional ignition cartridges.
The present invention can therefore be said, in summary, to consist of a method for initiating propellant charge modules for artillery guns comprising a predetermined amount of propellant powder enclosed in a preferably rigid cylindrical container which is made of a combustible material and is outwardly delimited by an outer cylinder wall adapted to the calibre dimensions of the intended artillery gun, two essentially plane gable walls defining its ends, and a centrally arranged inner cylinder wall which extends axially through the propellant charge module and which there forms a relay ignition channel. A characteristic feature of the invention is that there is arranged inside the relay ignition channel, in its central part as seen in the longitudinal direction, and at equal distance from the ends of the charge, a firing charge in the form of a number of firing charge rings which are arranged one after another in succession and bear against each other and whose outer dimensions match the inner dimensions of the relay ignition channel, and whose inner dimensions form a common inner ignition channel. At their gable ends facing each other, these firing charge rings are provided with spacing members in the form of studs, nibs or radial waves made in one piece with, and of the same material as, the firing charge rings. The spacing members in turn give rise to narrow ignition gaps of preferably 0.5-2 mm between the different firing charge rings. These firing charge rings with ignition gaps arranged between them have the task of ensuring an extremely fast burn-through of the material constituting the wall of the ignition channel and thus also ignition of the propellant powder included in the charge. With this type of firing charge, it is possible to ensure that the firing of the propellant powder in the main charge always takes place via the central channel, which in turn makes it possible to use the same charges in similar guns, even if these have slightly different chamber sizes. The initiation takes place so quickly that a flash-over ignition from outside never has time to take place, even if there is a sufficient gap between the chamber wall and the propellant charge for this to be able to take place in theory. To afford satisfactory functioning even in artillery guns intended for long ranges, in which there are many charge modules per charge and primarily where these are provided with laser firing systems, it has however been found that it is also necessary to take other measures which, according to the present invention, means that each charge module at respective ends of the relay ignition channel is provided with special initiating charges which guarantee a flash-over ignition between the charge modules and an ignition of the firing charges. These initiating charges must in this case consist of an easily combustible pyrotechnic substance, and as such we prefer those in which the main component is black powder.
According to one variant of the invention, the cylinder wall which forms the relay ignition channel and which delimits the space intended for the actual propellant powder charge from the central relay ignition channel is provided with a number of through-slots or holes for accelerating the actual burn-through.
In addition, this cylinder wall will preferably consist of at least 70% nitrocellulose while the firing charge, i.e the firing rings, and the alternative firing pill will preferably consist of a pyrotechnic composition produced by wet mixing and including 60-70% potassium nitrate, 20-30% boron and 10-15% zinc stearate and finally 4-10% of an acrylic binder.